1. Field of the Invention
This invention relates to a switching system and in particular to such systems for use with computer data loop terminals and to methods of operating the same.
2. Discussion of the Prior Art
This invention is typically applicable to data collection systems employed in department stores or the like where a central computer or controller communicates with a number of different kinds of data terminals such as point of sale terminals, ticket units and display/printer stations. Details of such systems are described, for example in IBM 3650 Retail Store System Installation Manual -- Physical Planning, GA 27-3074-1, File No. 3650-15, Copyright International Business Machines Corporation 1973, 1974. Collected data is subsequently processed in accordance with the needs of the installation. In such installations, the data terminals are connected in a number (typically three) of loops with respect to the central controller with each loop containing a plurality of terminals (typically 20 to 65) connected in series. The beginning and end of each loop are connected to the controller. It is known and typical to provide a series of subloops within each loop where each subloop may contain at least four data terminals.
Reference should be made to FIG. 1 where there is shown a single loop indicated at 100 having a plurality of subloops indicated at 102, 104 an 106. As is known but not typical, one data terminal may be associated with each subloop. The terminals are indicated at 108, 110 and 112. The beginning 114 and end 116 of loop 100 connect to a computer or controller 118. Thus one end of each subloop is associated with a data terminal while the other end is disposed at a location, which preferably is near the controller 118. Disposed at this location is a telephone type wiring terminal box indicated by dotted lines at 120. Disposed within the box are a plurality of manually removable clips 122 - 132, each loop having associated therewith two of the clips. Manually removable jumper cables 134 and 136 are also provided to complete the electrical connections between the subloops.
The sublooping arrangement is provided to facilitate more efficient usage of a loop. If a fault occurs within a data terminal, the controller will indicate fairly accurately which terminal is in need of repair. However, if the fault is, for example, located within the wiring to or from a terminal, the the controller may only indicate that a fault has occurred within the loop. Since the entire loop becomes inoperative upon the occurrence of a fault and since some loops may have as many as 65 or even more data terminals, an inoperable or down loop can become quite expensive. In particular, the data which normally would have been entered into the system through the data terminals must be preserved for later entry. Depending on the number of terminals and the activity at the terminals, it may take 20 - 40 (for example) hours to subsequently enter the data for each 1/2 hour the loop is down. Since this may be done on an overtime basis and since there may be a number of such occurrences, it can be appreciated how an accummulation of these occurrences would be extremely expensive.
By using the arrangement of FIG. 1, it is possible to short out the faulty subloop once it is located. Thus, if it is required to short out subloop 104, clips 126 and 128 may be removed and a jumper cable (shown in dotted lines) may be connected as shown in FIG. 1. This will have the effect of isolating loop 104 and restoring loop 100 so that data may be entered into terminals 108 and 112 while terminal 110 is either being repaired or replaced. Thus, the loop operation is rendered more efficient upon occurrence of a fault.
However, there are various shortcomings of the FIG. 1 arrangement and the other arrangements employed in the prior art. In the FIG. 1 arrangement, it is quite difficult for untrained personnel to properly remove clips and insert a shorting jumper cable with correct polarity and thereby effect removal of a terminal. Further, it should be understood that, for ease of illustration, loop 100 of FIG. 1 comprises a single wire in and out of each data terminal. However, generally, more than one such wire is employed and the number of clips and jumper cables increases directly with the number of wires added. Thus, the difficulty and resulting confusion as to proper connection and polarity thereof also directly increases whenever a multiple wire arrangement is used. Thus, quite often, valuable time is lost whenever such an untrained person attempts this procedure. Thus, it is preferable to have a technically trained person continuously available for such emergencies. However, this is usually not expedient and even when available, the FIG. 1 arrangement can still be difficult for a technician to manipulate especially when multiple wire arrangements are involved. Sometimes when a qualified technician is not on hand, the data terminal itself is unplugged from its respective jacks at a terminal location. A short circuiting plug is inserted in place of the terminal, rather than having the loop section itself shorted out. Using the short circuiting plug, however, puts two loop sections in series and lengthens the wire section between two working terminals. This can result in data loop resistance limits being exceeded resulting in possible garbled or no data input to the central computer.
As already indicated, it is industry practice for computer data loop terminals to be connected in a series loop arrangement, in a more or less random manner, dependent on the physical locations of terminals and the length of the "run" of wire or cable serving them. Under this practice, data loop wiring tends to proliferate and section lengths between data terminals tend to lengthen as time passes by. These tendencies develop as data terminals are added, moved or taken out of service.
Data loop wiring patterns are as numerous as the existing physical terminal loops multiplied by the number of people engaged in implementing these provisions. No particular pattern exists or is readily evident. Consequently, each installation of data loop wiring develops in a somewhat different pattern, and changes significantly with time because of the moves, additions, and disconnections of data terminals assigned to that loop. As a result, these wiring patterns become complex and time consuming to even those technicians who have worked on them before. They are even more so to the technicians who are called to work on them for the first time.
Efficient computer operation requires data terminals to be moved, added disconnected or "worked on" because of trouble either in a data terminal or in its serving wires. As indicated above the complexity of the wiring requires specially trained people to work on changes in the wiring pattern or on the clearing of trouble. Many times these men are not instantly available and operating inefficiencies continue until they arrive on the scene and finish the task they have been called on to perform. Many times an individual wire trouble serving a single data terminal will result in all data terminals on the same loop being out of service, if technical people are not available to analyze and correct such a situation, all data terminals on that loop are useless pending the arrival of the technician.